1. Field of the Invention
The present invention relates to an integrated circuit for an air bag system utilizing a bus system and a method for controlling operation of an air bag system using the same.
2. Description of Related Art
An airbag system for protecting a passenger from an impact at a time of a collision of a vehicle is indispensable, and the air bag system needs to be reduced in weight from a demand for reducing weight of n entire vehicle. Recently, types and total number of air bags such as an air bag for a driver side, an air bag for a passenger side next to the driver, an air bag for a rear seat side, and an air bag for a side impact are increasing, and therefore, a lighter air bag system is in greater demand.
In a current air bag system, an electronic control unit (ECU) connected to a power source (a battery installed in a vehicle) and an impact detecting sensor are individually connected to individual gas generators (a gas generator and an air bag are accommodated in a module case M as shown in FIG. 13). An aspect of the connection between the ECU and the individual gas generators is shown in FIG. 13.
As shown in FIG. 13, the ECU and an igniter (141 as shown in FIG. 14) of each of the individual gas generators are necessarily connected to each other through two conductors, and thereby, conductors double the number of the total number of igniters are required. Having many conductors contributes largely to weight increase in an air bag system. In view of constraints at a time of assembling vehicle parts, the ECU and the individual gas generators are not connected by only the conductors but connected by connecting a plurality of conductors via a plurality of connectors, and thereby, there occurs a serious problem such as a weight increase due to use of the connectors and a cost increase due to increase of the number of the connectors. Further, increase in volume (weight) of the ECU due to increase in volume of a capacitor incorporated into the ECU as a backup power source for activating all the igniters (serving at a time of a disconnection between the power source and the ECU) is another serious problem.
In view of the above, a trial for reducing a conductor weight required for connection between the ECU and the individual gas generators by utilizing a bus system in the air bag system has been examined.
An air bag system is constituted by providing bus lines comprising a plurality of loop wires passing through the ECU and connecting each of the individual gas generators to the bus line through two conductors (three or more conductors when occasion demands). In a case of such an air bag system, since only gas generators required corresponding to a collision situation of a vehicle are activated, an integrated circuit receiving information transmission from the ECU and a capacitor supplying a current for activating an igniter are provided in each of the individual gas generators. In the case of utilizing a bus system, the total number of capacitors is increased, but since the capacitors are distributed and arranged in the ECU and the respective igniters, the capacitance and weight of the capacitor per igniter is reduced. As a result, since the weight of the capacitors in this case is remarkably reduced as compared with the weight of the capacitors for backup in the air bag system shown in FIG. 13, a large weight reduction is achieved as the system as a whole in addition to largely reducing the amount of use of conductor, which is expected to be put in a practical use in the air bag system. Incidentally, there have been known JP2000-241098A, JP2000-513799A, and Japanese Patent No. 2707250 as the prior art utilizing the bus system.